The present invention relates to an endless belt transporting apparatus applied for an image carrying member or a transfer unit in an image forming apparatus, such as a copying machine or a printer.
With an image forming apparatus, such as a xerography machine, a photo receptor belt is employed as an image carrying member, a latent electrostatic image formed on the belt is developed with toner, and the developed toner image is transferred onto a paper placed on a transfer belt.
To prevent image quality of the developed image from deteriorating, it is very important to obtain a necessary flatness of the photo receptor belt and the transfer belt in the charging, exposure, developing, and image transferring stages. Generally, with a conventional endless belt transporting apparatus, while the necessary flatness is obtained by supporting endless belts of the photo receptor and transfer belts by means of a plurality of rolls or bars provided in the apparatus, an irregular motion of the endless belts are also suppressed by tensioning the belts. Further, to obtain the flatness, a planar or convex member is disposed so as to entirely contact a reverse surface of the belt.
However, side edge portions 1a of the endless belt 1 tend to curl in free state, as shown in FIG. 14. Further, when the endless belt 1 is supported on a flatness correcting member 3 provided between support frames 2 and formed of a roll or bar, the curled side edge portions 1a are deformed into minute bulges 4 which extend into a flatness area of the belt. Therefore, problems of deteriorating image quality are caused.
The requirement for obtaining the flatness of the endless belt is more important in the case when the endless belt is an image carrying member, and slit-like latent electrostatic images are formed over a latent electrostatic image already formed on the image carrying member by a pattern exposure unit, so that a tone reproduction performance of a photograph image is improved.